My niece worked at a national upper end restuarant chain a couple summers back. She said some waitreses who got ticked off at picky/demanding customers spit in the food all the time.
I'm always nice to the restuarant help.
Those that mock and become stupid at restaurant help, at the drive through or whatever, are really stupid. Never piss off those preparing your food. That’s just asking for it.
I personally just stay away from public eating places whenever possible.